In the last hundred years the method for storing perishable foods has undergone a remarkable change. Perishable foods were originally smoked, salted, dried or canned in an effort to preserve them for future use. As the industrial revolution progressed and cooling devices were invented, the preservation of perishable foods turned to the use of freezing as a storage and preservation technique. In particular, the meat processing industry grew to rely more heavily on large, centralized meat packing plants where meat was cut and then placed in large freezing facilities for subsequent distribution to wholesalers.
Early on in the meat packing industry it was discovered that packing raw or slightly cooled meat into boxes for freezing could cause meat spoilage if the boxes were packed too closely together such that the most interior box was insulated from the cooling environment by the outer product. That is, an interiorly located box would not be adequately cooled and the meat therein would spoil in transit. To eliminate the problem of self insulation, wood pallets were used as spacers to stack the boxes in a spaced apart relationship such that the cooled air of the freezer could circulate in and around the boxes. Wood pallets worked well; however, wood was not very efficient in conducting or transferring thermal energy. It was later learned that pallets made out of aluminum decreased the time in which it took to freeze the boxes of meat to the temperature desired. The aluminum pallets cooled the containers approximately 30% faster than did the wood pallets.
At least as early as the mid-1970's, spacer devices were formed out of aluminum for use in meat packing freezers. This spacer device was made of a heavy, rigid aluminum and it was formed of U-shaped channels that had ridges on the upper surface that supported the containers. The U-shaped channels had sidewalls that terminated in flanges that extended outwardly. These flanges were then connected to the flanges of a second set of U-shaped channels that were inverted and disposed transversely of the first set so that at the points of intersection channels opened up into one another. This aluminum pallet did increase the thermal transfer between the environment and the container for more rapidly cooling the containers to the freezer temperature. However, this aluminum spacer had disadvantages. The ridged surface presented less contact surface against the container thus limiting the amount of thermal transfer from the spacer. The gauge of aluminum used to achieve the strength necessary to support the boxes was fairly heavy, the weight of the spacer was also increased by the depth of the U-shaped channels which had sidewalls of approximately one inch in height; therefore, the spacers were massive and clumsy. Also, the flanges were of a narrow width that allowed deformation when riveted together. These deformed flanges often caught and snagged the boxes and containers that were placed on the spacer device.
To avoid some of the difficulties associated with the earlier aluminum spacers, another prior art construction was developed. This second aluminum spacer had a first set of U-shaped channel pieces and a second set of U-shaped channel pieces that were disposed at right angles to one another, but the flanges were eliminated. One set of channel pieces had a portion of the sidewall cut out so that the second set of channel pieces fit securely within the first set of channel walls. This arrangement was somewhat reminiscent of the corner saddle-notch for log cabins. This second construction utilized a lighter weight aluminum which cooled the containers more efficiently than did the ridged, thick aluminum spacer. However, it had several new disadvantages. One, the boxes tended to deform and snag on the channel rims since it was raised to a height that allowed contact with the container if the container is heavy enough to cause the spacer to bend slightly. The sidewalls had to be greater than 5/8 inch in height to accommodate the saddle notch construction. Also, the saddle-notches were difficult to secure and required an expensive welding step in fabrication. Finally, since the intersecting channels were arranged to lie within the open channel, less circulation of the air was permitted and this decreased the efficiency of the thermal transfer of energy.
Thus, there remained a need for a lightweight metal spacer that has open channels and a flat contact surfaces to maximize the efficiency of the thermal transferring surfaces. Further, there is a need for a spacer device which reduces the incident of snagging containers supported thereon. There is also a need for a lightweight channel system that can efficiently transfer heat and act as a heat sink while being of sufficient structural strength to maintain its shape under the weight of the supported containers.